Method of assembly of modular reservoir with integral compressible sealing strips and expansion joint

ABSTRACT

The water tank comprises a number of peripherally disposed modular wall components, each modular wall component defining a radially inner exposed surface, for direct engagement with the water inside the water tank, and a radially outer form-work area, for receiving liquid concrete to be cured. An integral hinge edgewisely interlocks each pair of successive modular wall components. An expansible joint is mounted into each hinge, wherein the expansible joint cooperates with the hinge so as to releasably interlock the modular wall components in their peripherally disposed fashion. The expansible joint provides a water tight seal at the hinge when soaked in water for a sufficient period of time. A second bevelled seal joint is further mounted against the hinge adjacent each wall component inner exposed surface spacedly from and radially inwardly from the expansible joint. Both first and second seal joints are for direct liquid engagement with the water tank water. A biocide agent is integrated within the radially outward second seal joint, wherein bacterial/fungus contamination of the water tank water is mitigated.

BACKGROUND OF THE INVENTION

It is known to provide an assembly of extruded thermoplastic structural components for use in the construction of the upright side walls of a modular building, for example schools, residential buildings, and the like. Each of these structural components includes an elongated rigid sheet member having at least two spaced-apart edges and provided with at least two integral lengthwise rail members located near corresponding edges thereof, a few of the structural components being releasably slidingly interlocked with one another about their rail members, without tools being required, to form hollow elongated panels. Each hollow panel defines a main body including a flat exterior face and a flat interior face, and circumscribes a generally closed inner enclosure cell, the hollow panel releasably interlocking with adjoining hollow panels successively to form a continuous wall structure. The structural components include first and second flat wall structural components and first and second elbowed corner structural components, the first elbowed corner structural component having opposite end edges and an intermediate corner edge and being provided with at least three spaced-apart integral lengthwise rail members located near the respective end and intermediate edges thereof. The inner cell is destined to receive concrete to be poured therein and the hollow panel body is adapted to withstand the load of a column of concrete poured therein. The position of one of the structural component relative to the other adjacent structural components is slidingly adjustable along the rail members.

However, such known extruded thermoplastic structural components are not as effective for the manufacture of water tanks, since there remains a vertical gap within the hinge formed between each pair of successive structural components. Contaminants such as bacteriae and fungus may build up within this hinge, thus possibly compromising the potable quality of water inside the tank. Unfortunately, this gap between the extruded thermoplastic structural components is required to enable the assembly thereof. Indeed, the usual method of assembly of extruded thermoplastic structural components is to vertically interlock each successive pair of such structural components by slidingly engaging same at their meeting corner portions. It is not currently possible to efficiently generate thermoplastic walls being totally smooth and without any gap between each successive pair of such structural components.

Moreover, the joints between structural components may not prevent accidental water leakage from the water tank into the radially outward concrete walls that support the water tank, which could reduce the useful life time of this supporting concrete structure. The water tanks should be water-tight, and the plurality of sealing joints between the structural components means that it is not cost-effective to individually seal all these joints once the tank structure has been set.

SUMMARY OF THE INVENTION

The invention relates to an assembly of extruded structural modular wall components for use in the construction of the upright side walls of a water tank, each of said wall components including an elongated rigid sheet member having two integral lengthwise rail members located near corresponding opposite edges thereof, said wall components being releasably slidingly interlocked with one another about their rail members at hinge means to form hollow elongated panels; each hollow panel defining a main body including a flat inner exposed surface, for direct engagement with the water inside the water tank, and an opposite outer formwork area, for receiving liquid concrete to be cured, a hollow panel releasably interlocking with adjoining hollow panels successively to form a substantially continuous wall structure circumscribing a generally closed water receiving enclosure; and further including first seal barrier means, mounted into each hinge means; wherein said first seal barrier means defines an inoperative condition, and an operative condition where both structural integrity and waterproofness of the water tank are achieved.

Preferably, a second seal barrier means is mounted about said hinge means adjacent each said wall component inner exposed surface spacedly from said first seal barrier means, said first and second seal barrier means for direct liquid engagement with the water tank water; wherein said second seal barrier means cooperates with said hinge means to provide a continuous wall structure when said hollow panels are interlocked with one another in successive pairs.

A biocide agent could be integrated with said second seal barrier means, wherein contamination of the water tank water is mitigated. Preferably, said biocide agent is selected from the group comprising Phenoxarsine®, Fungitrol and Nuocide (the latter two being made by International Specialty Products, New Jersey, USA) at a concentration preferably less than 0.1% by weight of the total weight of said second seal barrier means.

In one embodiment, said hinge means includes a male rail element from a first said modular wall component, and a female rail element from a second said successive modular wall component, said first seal barrier means mounted inside a cavity defined by said female rail element.

Preferably, said first seal barrier means is an expansible joint, engaged into and occupying a small fraction of said female rail element cavity in said inoperative condition thereof, but completely filling up said female rail element cavity in said operative condition thereof; said second seal barrier means being less effective in waterproofness than said first seal barrier means so that water being filled into the water tank is allowed to seep partly around said second seal barrier means and reach said first seal barrier means. In said operative condition of said expansible joint, said male element could wedge a leading edge portion thereof being exposed to the water from the water tank water exclusively from the remainder of said expansible joint, said expansible joint leading edge portion being small relative to the overall volume of said expansible joint.

Preferably, said expansion joint is made from at least one organic ingredient and from an inorganic ingredient. Said organic ingredient could comprise a hydrophilic resin. Said hydrophilic resin could be selected from the group comprising polyacrylamide, acrylic polymer and polyurethane foam. Said organic ingredient could also further comprises a thermoplastic rubber compound, preferably selected from the group comprising ethylene propylene diene, chloroprene, and polyisoprene. Said inorganic ingredient could be a filler selected from the group comprising calcium carbonate, calcium chloride, silicium dioxide and bentonite.

In one embodiment, said second seal barrier means forms a sealing strip having a hardness value ranging between 45 and 65 on the SHORE D scale, while said modular wall components have a hardness value ranging between 75 to 85 on the SHORE D scale, said second seal barrier means sealing strip being added by coextrusion to the corner portion of each modular wall components. Said second seal barrier means could provide redundancy to the sealing features of the first seal barrier means, for example if the first seal barrier means becomes accidentally damaged during erection of the water tank and associated seal barrier means.

The invention also relates to a method of assembly of a water tank of the type where the water tank comprises a number of peripherally disposed modular wall components, each modular wall component defining a radially inner exposed surface, for direct engagement with the water inside the water tank, and a radially outer formwork area, opposite said inner exposed surface, for receiving liquid concrete to be cured, hinge means edgewisely interlocking each pair of successive said modular wall components, and first seal barrier means, mounted into each said hinge means; wherein said first seal barrier means cooperates with said hinge means so as to releasably interlock said modular wall components in their peripherally disposed fashion, said first seal barrier means defining an inoperative condition, and an operative condition where both structural integrity and waterproofness of the water tank are achieved; wherein said first seal barrier means is an expansible joint, engaged into and occupying a small fraction of said female element cavity in said inoperative condition thereof, but completely filling up said female element cavity in said operative condition thereof; said second seal barrier means being less effective than said first seal barrier means so that water from said tank is allowed to seep partly around said second seal barrier means and reach said first seal barrier means; the method comprising the following steps: inserting said expansible joint into said hinge means; tilting each pair of successive first and second said wall components relative to one another by a small acute angle (preferably of between 15 to 25 degrees), vertically sliding facing edge portions of said each pair of first and second wall components about said hinge means; tilting back said first and second wall components to a coextensive substantially planar condition; filling up water inside the water tank, wherein said expansible joint comes to be soaked with water; and allowing water to expand said expansible joint, until a completely water tight hinge means is achieved.

The method could also be such that a second seal barrier means would be added, forming a deformable non expansible bevelled joint, the latter joint forming an exposed slanted edge surface, wherein the method further comprises the additional following steps of: before said step a), inserting said bevelled joint into said hinge means, and fixedly securing said bevelled joint against said hinge means radially inwardly of said expansible joint; and between steps d) and e) cushioning this tilting back step by cooperative action of deforming motion of said bevelled joint about its slanted edge surface.

Preferably, the method also includes a step between steps a) and b) of fixedly securing said first expansible joint to corresponding wall components within said hinge means, wherein said expansible joint securing means is selected from the group comprising friction fit interlock with said wall component within said cavity, coextrusion during manufacture thereof, and application of a glue compound fixedly interconnecting said expansible joint to said wall component within said cavity. The expansible compound could also be applied by a caulking gun

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top edge plan view of a number of prior art upright rigid thermoplastic structural components forming a fraction of the side walls of an upright upstanding wall;

FIG. 2 is a top edge plan view of one rigid L-shape structural component similar to those of FIG. 1, and further showing a soft thermoplastic bevelled seal joint made by coextrusion along an interior corner thereof;

FIG. 3 is an enlarged view of the corner portion of FIG. 2, and further showing the expansible seal joint;

FIGS. 4 and 5 are top edge plan view of a pair of interlocking L-shape structural components of FIG. 2, showing the two seal joints of FIG. 3, and sequentially suggesting how these two structural wall components become interlocked in fluid tight fashion;

FIG. 6, on the third sheet of drawings, is an enlarged view of the partly interlocked portion of the pair of L-shape structural components of FIG. 4;

FIG. 7, on the second sheet of drawings, is an enlarged view of the fully interlocked portion of the pair of L-shape structural components of FIG. 5;

FIG. 8 is a perspective view, at a smaller scale, of the expansible seal joint of FIG. 3;

FIG. 9, on the last sheet of drawings, is a view similar to FIG. 3, but with the expansible seal joint in friction fit interlock with the PVC structural component;

FIG. 10 is a view similar to FIG. 9, but with the expansible seal joint being fixedly secured by a glue component to the PVC structural component; and

FIG. 11 is a partly broken plan view of a PVC structural component, clearly showing _(t)hat the expansible seal joint is a single monolithic “stick” extending along the full length of the PVC structural component.

DETAILED DESCRIPTION OF THE EMBODIMENT OF THE INVENTION

The present invention is therefore directed to improving upon existing assemblies of extruded thermoplastic structural components for modular reservoir constructions, and in particular for potable water tank applications and for pisciculture (for example, for salmon farms).

FIG. 1 shows a prior art section of upright wall assembly 10, made of two L-shape extruded PVC structural components 12, 14 interlocked with flat extruded PVC structural components 16, 18. L-shape component 12 includes a first wall 20 and a second wall 22 generally perpendicular to one another, while L-shape component 14 similarly has a first wall 24 and a second wall 26 generally perpendicular to one another. The exterior PVC layer face 20A, 24A of each walls 20, 24, respectively typically includes a higher quality PVC material, and is adapted to be the exposed face at the interior of a water tank T. Each outer end of L-shape legs 22, 26, form a rail member 28, 30, respectively, of a design enabling transverse interlock of two opposite exterior legs 16, 18. The opposite ends of L-shape legs 22, 24, form elbowed lips 32, 34, respectively, and the intermediate section of legs 22, 24, form rail members 36, 38, respectively, of a design enabling transverse interlock of one lip 34 from one L-shape component 14 with one rail member 36 from another L-shape component 12. The free end tip 32A, 34A, of each lip 32, 34, is also bevelled.

Accordingly, an interior gap 40 remains between interlocked lip 34 and adjacent leg 36A from rail member 36, with gap 40 facing the interior of water tank T. A fluid passageway 41 is formed between interior gap 40 and the formwork cell C opposite the interior of water tank T. Panels 16, 18, each include at opposite ends elbowed lips 42, 44, and 46, 48, respectively, which are similar to lips 32, 34 but inverted relative thereto. Each pair of registering lips of panels 16, 18, say lips 44, 48, are able to interlock with complementary sections of L-shape outer end rail member, say rail member 28.

In FIGS. 2 and 3, there is shown an L-shape structural component 12, with a radially inwardly located soft sealing strip 50 being added to the exposed surface of leg 36A of rail member 36. Soft sealing strip 50 is preferably PVC, and strip 50 is factory installed to leg 36A by co-extrusion process. As best shown in FIG. 3, PVC strip 50 includes an exposed outer surface 50A which is bevelled, i.e. that PVC strip 50 has a thicker portion adjacent interior surface wall layer 20A of panel 20, which progressively becomes thinner as one moves away from surface layer 20A. PVC strip 50 should extend for a large fraction of and not excluding all of the height of upright leg section 36A of upright L-shape component 12.

Two different levels of hardness are used for manufacture of the thermoplastic (preferably polyvinyl chloride or PVC as it is cheaper and easier to handle) components of the present invention: the standard “rigid” hardness level for most of the PVC component, preferably varying between 75 and 85 on the SHORE D scale, and being most preferably of a hardness value of about 79 on the SHORE D scale and a lower “flexible” hardness level, preferably varying between 45 and 65 on the SHORE A scale, and being most preferably of a hardness value of about 55 on the SHORE A scale, for a radially inward sealing strip 50 (detailed hereinbelow) added by coextrusion to the corner portion of each L-shape extruded PVC structural component 12. (For context purposes only, a residential window frame is made of rigid PVC, while the flexible sealing lips between this window frame and the corresponding window glass are made from flexible PVC) The purpose of this radially inward sealing strip 50 is to therefore seal the above-noted gap between two above-noted successive structural components, to prevent passage of microbial contaminants such as bacteriae, fungus or mold, without hampering ease of assembly of the PVC structural components to form a modular wall construction.

PVC strip 50 has memory shape, i.e. it will hold its own bevelled shape in unbiased condition, but will be able to deform under compressing force, such as when elbowed lip 34 engages with leg 36A as suggested in FIG. 7 and is tilted thereagainst. In FIG. 7, it can be seen that the shape of sealing strip 50 has changed from bevelled to generally ovoidal, and that the gap 40 facing the interior of the water tank T has been closed in partly fluid-tight fashion. However, passageway 41 still opens freely at the opposite end into formwork cell C. Seal strip 50 should extend the full height of the modular wall component 12.

The size of unbiased bevelled soft PVC strip 50 should be such that the thicker section thereof is slightly wider than the width value of gap 40, and that the thinner section thereof is slightly narrower than this width value of gap 40, so that upon deformation of PVC strip 50 under biasing load from engagement of leg 36A of rail member 36 into the hollow of elbowed lip 34, (FIG. 7) a partly water-tight sealing interengagement is achieved between leg 36A and lip 34 via soft PVC strip 50 closing gap 40.

Preferably, a biocide agent effective against at least bacteriae and/or fungus, is factory admixed with the compound of expansion joint 49. This biocide agent could be for example Phenoxarsine®, Fungitrol® or Nuocide , but in those cases, should be at a very low concentration, preferably less than 0.1% in weight as of total weight of the expansion joint 49, in view of chemical toxicity issues for the marine life inside water tank T. Accordingly, no microbiological contaminant is allowed to enter gap 40 before water fills water tank T. Radially inwardly located sealing strip 50 being in constant direct contact with water from the tank T when the latter is filled up with water, strip 50 cannot and does not incorporate a biocide agent in view of the above-noted chemical toxicity issues that may arise with the fish inside the water tank T. On the other hand, although expansion joint 49 in unexpanded state comes initially in contact with the water from the water tank T, once joint 49 achieves its fully expanded operative condition due to water from water tank T soaking same during its expansion, radially outward joint 49 becomes substantially shielded from water coming from water tank T by radially inward sealing strip 50, so that on a long term continuous basis after full expansion of expansion joint 49, chemical leaching of biocide agent from radially outward expansion joint 49 in a direction radially inward toward the water of water tank T will be substantially prevented by radially inward sealing joint 50.

Preferably, the interior face layer 20A, 24A, of legs 20, 24, could be of higher quality rigid PVC, while the remainder of components 12, 14, 16 and 18 (except soft PVC strip 50) could be made of lower quality (e.g. made from recycled material) rigid PVC.

FIGS. 4 to 6 shows that, contrary to conventional interengagement of each successive pair of PVC components, where rail member 36 and elbowed lip 34 are interlocked in sliding motion with panel 22 remaining perpendicular to legs 20 and 24 during the sliding motion, in the present invention, panel 22 must be first be tilted by a small acute angle, preferably ranging between 15 and 25 degrees, and most preferably of about 20 degrees, before vertical sliding motion is performed, to accommodate free passage of added strip 50. This tilted sliding motion is facilitated by the bevelling of slanted edge of lip tip 34A. Once rail member 36 and panel lip 34 are fully inserted into one another, then panel 22 is tilted back to its final condition perpendicular to panels 20 and 24, as illustrated in FIG. 5. It is only after panel 22 has reached its position orthogonal to panels 20 and 24 that outer panels 16 and 18 (opposite water tank T) can be interlocked to transverse rail member 28 at end lips 44 and 48 thereof. At this stage, passageway 41 is not sealed at its end opening into formwork cell C (into which fluid concrete will be poured for water tank support).

Also, sealing strip 50 could optionally provide some level of thermal adjustment, so as to act as an expansion joint in climates where there are substantial fluctuations between night and day, wherein cyclical dilatation and retraction of the sealing joint 50 would be accommodated.

As shown in FIGS. 3 to 10 of the drawings, expansion joint 49 is further added to provide a complete water tight seal into cavity 51. Expansion joint 49 is radially outwardly located relative to radially inward seal joint 50 and spacedly therefrom. Expansion joint 49 is made from at least an organic ingredient and an inorganic ingredient. Preferably, the organic ingredient comprises a hydrophilic resin, selected from the group comprising polyacrylamide, acrylic polymer and polyurethane foam; and/or a thermoplastic rubber compound, selected from the group comprising ethylene propylene diene, chloroprene, and polyisoprene. Preferably also, the inorganic ingredient will be a filler selected from the group comprising calcium carbonate, calcium chloride, silicium dioxide and bentonite.

Examples of such expansible seal joints 49 include:

-   -   the CCW MiraSTOP™ seal from Carlisle Coatings & waterproofing         (Wylie, Tex.);     -   the Hydrotite™ seal distributed by Greenstreak (St-Louis, Mo.);     -   the Swellseal™ distributed by Construction Chemicals inc.         (Houston, Tex.);     -   the SikaSweel-A™ seal from Sika Canada inc. (Mississauga,         Ontario, Canada), and manufactured in Europe;     -   the HydroSeal HW-0520™ from Specton Construction products ltd         (Acton, Ontario, Canada), and manufactured in the United States;     -   the Idrostop, manufactured by Mapei in Italy.

Expansible joint 49 is installed into cavity 51 either at the factory, or in situ where the water tank is to be mounted. When this joint 49 comes in contact with water, in particular when water is filling up inside the water tank T, the joint 49 will expand by between 100% and up to 800%, so as to completely fill the cavity 51 (with lip 34A engaged inside cavity 51, see FIG. 7) and thus provide a completely water tight assembly for the water tank T. Once water fills up water tank T, expansion joint 49 will come in direct contact with this water and will progressively expand from its initial unexpanded condition (FIG. 3 e.g.) to its fully expanded condition (FIG. 7) , typically within a period ranging between about 24 hours to a few to several days, depending on the seal make.

Expansible joint 49 will come in direct contact with water from water tank T since expansible joint 49 extends for the full height of the structural components 20, 24, . . . , as well as for the bevelled seal joint 50, but the latter provides only incomplete water seal.

According to one embodiment, expansion joint 49 is of the type where maintenance of its expansion is conditional upon continuous contact with water; expanded joint 49 will indeed progressively retract to its original unexpanded state upon soaking contact with water being removed.

The present assembly is made up of several structural components 12, 14, . . . having a width of for example 10 centimeters (cm) , circumscribing a water tank into which a very important volumic load of water is found, which must be accommodated for water sealing purposes. The present solution is furthermore cost-effective, since the expansible joint seal 49 can be of small overall relative size.

The installation of this sealing joint 49 can be done directly on the manufacturing line, by engaging this sealing joint 49 into cavity 51 transversely through cavity access mouth 52 (FIG. 3), and by maintaining this sealing joint 49 in place inside cavity 51 by appropriate securing means. According to one embodiment of the invention, shown in FIG. 9 of the drawings, this joint securing means will be a friction fit interlock of unexpanded sealing joint 49 at the opposite edges 53, 53′ thereof within cavity 51 with opposite facing seating surfaces 120, 122, of structural components 20, 22, respectively. Seating surface 122 extends through a plane opening into cavity mouth 52. According to an alternate embodiment of the invention, shown in FIG. 10, this securing means will be a glue compound 54 applied against the flooring surface 136 within cavity 51 opposite cavity access mouth 52.

FIG. 11 shows that for optimal performance, the expansion joint 49 should most preferably be a monolithic tube extending for the full height of the structural component 20, 24, to prevent accidental water leakage along its length, which would otherwise be the case if two or more separate such joint sticks would be staggered axially in end to end fashion. Seal joints 49 and 50 both abut at their bottom ends against the top surface of a supporting concrete ground slab. Another expansible joint, not shown, will be added between these latter bottom ends and the concrete ground slab. This latter another expansible seal joint could be for example the HydroSeal HW-0520™ from Specton Construction products ltd.

It is noted that the tilting action of each pair of structural components 20, 24, . . . , (performed either during on site assembly or in the manufacturing line) of the modular tank T as discussed above and sequentially illustrated in FIGS. 4 and 6, is not hindered by the expansion joint 49, since the latter remains unexpanded at this stage and thus readily allows the leg 34A to move tiltingly within cavity 51 toward but spacedly from cavity seat 136. Accordingly, the cross-sectional surface of joint 49 in its unexpanded initial condition (FIGS. 3 and 9-10) should represent a small fraction of the total internal area of cavity 51, as illustrated, for example less than half of this interior area of cavity 51, so as to enable free vertical sliding motion of the extruded structural components 20, 24, . . . with one another during assembly. On the other hand, in the fully expanded condition of joint 49′ (FIG. 7), the cross-sectional surface of joint 49′ would fill all the internal area of cavity 51, in such a way as to provide a completely liquid tight seal between structural component lip 34 and expanded state joint 49′.

Alternate methods of installation would be either caulking gun application or by co-extrusion of the expansion joint 49 during manufacture of the structural components 20, 24. This would be very efficient, however it would require substantial overhead costs as well as frequent adjustments along the production line.

In operation, with the water tank T being progressively filled with water, radially outward unexpanded joint 49 comes in direct liquid contact with water from water tank seeping through cavities 40 and 51, and around non completely water-tight radially inward seal 50, and joint 49 progressively expands reactively with soaking contact with water to eventually provide 100% water tight seal within structural component cavity 51 when fully expanded. Radially inward joint 50 will typically provide mainly a biocide barrier, rather than an effective water seal, so that no bacteria, mold or the like microbiological agent potentially harmful to the marine life inside the water tank T will be allowed to be accidentally transferred into the water tank T. Thus, the fish and/or other marine life inside the water tank T will be protected by the first inner seal barrier 50 in direct contact with the water tank water from any biohazard that could otherwise have been accidentally generated, while the second radially outer seal barrier 49 provides the 100% required water tight seal, to retain water inside the water tank T. Hence, both seals 49 and 50 remain in liquid contact with the water in the tank T, when the latter is filled with water. 

I claim:
 1. An assembly of extruded structural modular wall components for use in the construction of the upright side walls of a water tank, each of said wall components including an elongated rigid sheet member having two integral lengthwise rail members located near corresponding opposite edges thereof, said wall components being releasably slidingly interlocked with one another about their rail members at hinge means to form hollow elongated panels; each hollow panel defining a main body including a flat inner exposed surface, for direct engagement with the water inside the water tank, and an opposite outer formwork area, for receiving liquid concrete to be cured, a hollow panel releasably interlocking with adjoining hollow panels successively to form a substantially continuous wall structure circumscribing a generally closed water receiving enclosure; and further including first seal barrier means, mounted into each hinge means; wherein said first seal barrier means defines an inoperative condition, and an operative condition where both structural integrity and waterproofness of the water tank are achieved.
 2. A water tank as in claim 1, further including second seal barrier means, mounted about said hinge means adjacent each said wall component inner exposed surface spacedly from said first seal barrier means, said first and second seal barrier means for direct liquid engagement with the water tank water; wherein said second seal barrier means cooperates with said hinge means to provide a continuous wall structure when said hollow panels are interlocked with one another in successive pairs.
 3. A water tank as in claim 2, wherein said second seal barrier means is located radially inwardly from said first seal barrier means relative to the water tank.
 4. A water tank as in claim 3, further including a biocide agent, integrated with said first seal barrier means, wherein contamination of the water tank water is mitigated.
 5. A water tank as in claim 4, wherein said biocide agent is selected from the group comprising Phenoxarsine®, Fungitrol® and Nuocide®,and at a very low concentration relative to the total weight of said second seal barrier means.
 6. A water tank as in claim 4, wherein said hinge means includes a male rail element from a first said modular wall component, and a female rail element from a second said successive modular wall component, said first seal barrier means mounted inside a cavity defined by said female rail element.
 7. A water tank as in claim 6, wherein said first seal barrier means is an expansible joint, engaged into and occupying a small fraction of said female rail element cavity in said inoperative condition thereof, but completely filling up said female rail element cavity in said operative condition thereof; said second seal barrier means being less effective in waterproofness than said first seal barrier means so that water being filled into the water tank is allowed to seep partly around said second seal barrier means and reach said first seal barrier means.
 8. A water tank as in claim 7, wherein in said operative condition of said expansible joint, said male element wedges a leading edge portion thereof being exposed to the water from the water tank water exclusively from the remainder of said expansible joint, said expansible joint leading edge portion being small relative to the overall volume of said expansible joint.
 9. A water tank as in claim 8, wherein said expansion joint is made from at least one organic ingredient and from an inorganic ingredient.
 10. A water tank as in claim 9, wherein said organic ingredient comprises a hydrophilic resin.
 11. A water tank as in claim 10, wherein said hydrophilic resin is selected from the group comprising polyacrylamide, acrylic polymer and polyurethane foam.
 12. A water tank as in claim 11, wherein said organic ingredient further comprises a thermoplastic rubber compound.
 13. A water tank as in claim 12, wherein said thermoplastic rubber compound is selected from the group comprising ethylene propylene diene, chloroprene, and polyisoprene.
 14. A water tank as in claim 9, wherein said inorganic ingredient is a filler selected from the group comprising calcium carbonate, calcium chloride, silicium dioxide and bentonite.
 15. A water tank as in claim 8, wherein said second seal barrier means forms a sealing strip having a hardness value ranging between 45 and 65 on the SHORE D scale, while said modular wall components have a hardness value ranging between 75 to 85 on the SHORE D scale, said second seal barrier means sealing strip being added by coextrusion to the corner portion of each modular wall components.
 16. A method of assembly of a water tank of the type where the water tank comprises a number of peripherally disposed modular wall components, each modular wall component defining a radially inner exposed surface, for direct engagement with the water inside the water tank, and a radially outer formwork area, opposite said inner exposed surface, for receiving liquid concrete to be cured, hinge means edgewisely interlocking each pair of successive said modular wall components, and first seal barrier means, mounted into each said hinge means; wherein said first seal barrier means cooperates with said hinge means so as to releasably interlock said modular wall components in their peripherally disposed fashion, said first seal barrier means defining an inoperative condition, and an operative condition where both structural integrity and waterproofness of the water tank are achieved; wherein said first seal barrier means is an expansible joint, engaged into and occupying a small fraction of said female element cavity in said inoperative condition thereof, but completely filling up said female element cavity in said operative condition thereof; said second seal barrier means being less effective than said first seal barrier means so that water from said tank is allowed to seep partly around said second seal barrier means and reach said first seal barrier means; the method comprising the following steps: a) inserting said expansible joint into said hinge means; b) tilting each pair of successive first and second said wall components relative to one another by a small acute angle, c) vertically sliding facing edge portions of said each pair of first and second wall components about said hinge means; d) tilting back said first and second wall components to a coextensive substantially planar condition; e) filling up water inside the water tank, wherein said expansible joint comes to be soaked with water; and f) allowing water to expand said expansible joint, until a completely water tight hinge means is achieved.
 17. A method as in claim 16, further including a second seal barrier means, radially inwardly of and spacedly from the first seal barrier means and forming a deformable non expansible bevelled joint, the latter joint forming an exposed slanted edge surface, wherein the method further comprises the additional following steps of: before said step a), inserting said bevelled joint into said hinge means, and fixedly securing said bevelled joint against said hinge means radially inwardly of said expansible joint; and between steps d) and e) cushioning this tilting back step by cooperative action of deforming motion of said bevelled joint about its slanted edge surface. 18 A method as in claim 17, further including a step between steps a) and b) of fixedly securing said first expansible joint to corresponding wall components within said hinge means, wherein said expansible joint securing means is selected from the group comprising friction fit interlock with said wall component within said cavity, and a glue compound fixedly interconnecting said expansible joint to said wall component within said cavity, said glue compound applied by a technique selected from the group comprising use of a caulking gun and coextrusion on the manufacture line.
 19. A method as in claim 16, wherein said small acute angle has a value between 15 and 25 degrees. 